An American Navy veteran from California has been imprisoned in Iran since July on unknown charges, according to reports.

Michael R. White, 46, was arrested months ago while visiting his Iranian girlfriend, The New York Times reports. White should have boarded a flight on July 27 to leave Iran, but never did, mom Joanne White told the Times. She said she then filed a missing persons report with the State Department.

“All I know is that he is alive and they were putting in a request for a consular visit by the Swiss,” she told the Times.

The State Department said in a statement that it is aware of the reports of White's alleged detention but would not comment further "due to privacy concerns."

On Monday, an online news service run by Iranian ex-patriots, IranWire, reported that a former inmate spoke to White in prison, saying White told him he was arrested in late summer of 2018 as he and his girlfriend were about to fly out of Hasheminejad Airport in Mashhad. The man was quoted saying White wasn't in good psychological condition and also had a tumor that could be cancerous.

White had underwent chemotherapy and radiation for a neck tumor before his last visit to Iran, his mother told the Times.

She told CBS News that the last time she made contact with her son was July 13.

At least three other U.S. citizens are also being held in Iranian prison under espionage charges the State Department has denounced as “fabricated.” Chinese-American Xiyue Wang as well as Iranian-American businessman Siamak Namazi and his father, Baquer Namazi, are all serving 10-year sentences.